diff --git a/src/irda.c b/src/irda.c
index 833aaed..fba618c 100644
--- a/src/irda.c
+++ b/src/irda.c
@@ -72,7 +72,7 @@ struct irda {
 };
 
 
-int irda_errcode ()
+int irda_errcode (void)
 {
 #ifdef _WIN32
 	return WSAGetLastError ();
@@ -82,7 +82,7 @@ int irda_errcode ()
 }
 
 
-const char* irda_errmsg ()
+const char* irda_errmsg (void)
 {
 #ifdef _WIN32
 	static char buffer[256] = {0};
@@ -111,7 +111,7 @@ const char* irda_errmsg ()
 }
 
 
-int irda_init ()
+int irda_init (void)
 {
 #ifdef _WIN32
 	WSADATA wsaData = {0};
@@ -137,7 +137,7 @@ int irda_init ()
 }
 
 
-int irda_cleanup ()
+int irda_cleanup (void)
 {
 #ifdef _WIN32
 	if (WSACleanup () != 0) {
diff --git a/src/irda.h b/src/irda.h
index fa2ac78..7765b18 100644
--- a/src/irda.h
+++ b/src/irda.h
@@ -30,13 +30,13 @@ typedef struct irda irda;
 
 typedef void (*irda_callback_t) (unsigned int address, const char *name, unsigned int charset, unsigned int hints, void *userdata);
 
-int irda_errcode ();
+int irda_errcode (void);
 
-const char* irda_errmsg ();
+const char* irda_errmsg (void);
 
-int irda_init ();
+int irda_init (void);
 
-int irda_cleanup ();
+int irda_cleanup (void);
 
 int irda_socket_open (irda **device);
 
diff --git a/src/serial.h b/src/serial.h
index 80c3bb4..4b745e2 100644
--- a/src/serial.h
+++ b/src/serial.h
@@ -46,8 +46,8 @@ enum queue_t {
 	SERIAL_QUEUE_BOTH = SERIAL_QUEUE_INPUT | SERIAL_QUEUE_OUTPUT
 };
 
-int serial_errcode ();
-const char* serial_errmsg ();
+int serial_errcode (void);
+const char* serial_errmsg (void);
 
 int serial_open (serial **device, const char* name);
 
@@ -98,7 +98,7 @@ int serial_get_transmitted (serial *device);
 
 int serial_sleep (unsigned long timeout /* milliseconds */);
 
-int serial_timer ();
+int serial_timer (void);
 
 #ifdef __cplusplus
 }
diff --git a/src/serial_posix.c b/src/serial_posix.c
index 3063228..31ee758 100644
--- a/src/serial_posix.c
+++ b/src/serial_posix.c
@@ -62,13 +62,13 @@ struct serial {
 // Error reporting.
 //
 
-int serial_errcode ()
+int serial_errcode (void)
 {
 	return errno;
 }
 
 
-const char* serial_errmsg ()
+const char* serial_errmsg (void)
 {
 	return strerror (errno);
 }
@@ -687,7 +687,7 @@ serial_sleep (unsigned long timeout)
 
 
 int
-serial_timer ()
+serial_timer (void)
 {
 	struct timeval tv = {0};
 	if (gettimeofday (&tv, NULL) != 0) {
diff --git a/src/serial_win32.c b/src/serial_win32.c
index 89e9819..fcf6d6b 100644
--- a/src/serial_win32.c
+++ b/src/serial_win32.c
@@ -51,13 +51,13 @@ struct serial {
 // Error reporting.
 //
 
-int serial_errcode ()
+int serial_errcode (void)
 {
 	return GetLastError ();
 }
 
 
-const char* serial_errmsg ()
+const char* serial_errmsg (void)
 {
 	static char buffer[256] = {0};
 	unsigned int size = sizeof (buffer) / sizeof (char);
@@ -539,7 +539,7 @@ serial_sleep (unsigned long timeout)
 
 
 int
-serial_timer ()
+serial_timer (void)
 {
 	return GetTickCount ();
 }